Swivels and their use are well known. Swivels have commonly been used to connect together two lines or cables where rotation at the point of connection is desired. For example, when an electrical or telecommunications cable is being pulled through a conduit by the use of a pulling or fish line, the cable is typically unrolled off a large reel at one end of the conduit as it is pulled through. As the cable unrolls, it sometimes develops twists that, if not corrected, could damage the cable under the tension applied for long pulls. The use of a swivel between the end of the cable and the pulling line enables any such twists to be removed as the cable may rotate independent of the pulling line.
In other applications, a swivel is critical to the operation of combined underground boring and cable pulling. In this situation, a pilot hole is drilled through the underground structure where a cable is to be run. Once the pilot hole is completed, a drill steel is inserted back through the hole and a cutting head attached to the drill steel. The drill steel is then connected to a boring machine which drives the cutter, either through direct rotation or through the application of pneumatic or hydraulic pressure to motors on the cutter. Typically a cable, or in some instances a conduit or casing, is connected to the rear of the cutting head so that pulling the cutting head back through the pilot hole not only enlarges the pilot hole to the desired diameter but also serves to pull the cable or conduit as the hole is cut. Accordingly, since the cutting head is rotating to enlarge the pilot hole, in order to be able to pull a cable or conduit through the hole a swivel must form part of the connection between the cutting head and the cable or conduit.
Yet a further application of such swivels involves use on cables lifting, such as would be used on cranes or the like. When lifting objects with a crane it is usually desirable or necessary to be able to rotate the lifted object to facilitate movement or re-positioning. In order to prevent the application of rotational forces on the crane's lifting cable, line swivels are often incorporated on the harness or sling used to attach the crane cable to the object.
In each of the above applications, as well as in numerous others, the swivel must be designed to withstand the tensile force applied to it under use and must be able to operate in environments that may subject the swivel to water and dirt. For example, when used in underground boring applications the swivel will be directly subjected to water and dirt and may even be completely submerged in mud or debris at times. Similarly, when pulling cables through underground conduit, one often encounters conduits filled with water or mud. In lifting operations, line swivels are typically exposed to rain, sleet or snow and are often subjected to significant tensile loading.
Others have recognized these design criteria and attempted to develop line swivels capable of operating under such environments, and capable of withstanding the tensile loading to which they may be subjected, but have failed. In order to be able to withstand the load to which the swivel may be exposed, others have commonly increased the size of the components of the swivel, including ball bearing components as are typically used. While this may be one manner of approaching the problem, the result is sometimes a swivel too large in physical dimension for the desired task. In addition increasing the physical size of the swivel increases its weight and normally its cost.
Similarly the methods of sealing swivels against water and debris that have been used or proposed to date have met with limited success. The means of sealing that have been used are only effective under limited exposure in terms of both time and quantity of water and debris to which the swivel may be subjected, and comprise the use of a simple "O" ring seal.
The result of these shortcomings is that swivels currently in use have a significantly reduced operational life span when used in harsh environments. Once water or dirt penetrates into the interior of the swivel, corrosion, freezing in low temperatures, and reduced bearing life usually result. As well, significant tensile loading quickly causes ball bearings to fail or wear prematurely.